1. Field of the Invention
The present invention relates to a pretreatment agent for electroless plating, and a method for pretreating a substrate to be used for a printed wiring board using the same, and a process for producing a printed wiring board using the same. The pretreatment agent for electroless plating of the present invention is preferably used, in particular, as a pretreatment agent of a substrate to be used for a printed wiring board, which contains a silica-based filler in an insulating resin, before performing electroless plating on the surface of the substrate to produce a printed wiring board.
2. Description of the Related Art
The printed wiring boards widely used in the electronics and other fields may often be produced by any of the additive methods using electroless plating. The additive methods are roughly classified into full-additive methods in which wiring is formed by only electroless plating and semi-additive methods in which wiring is formed by electroless plating and subsequent electroplating. More specifically, the surface of an insulating resin substrate is roughened and then provided with a catalyst, followed by electroless plating such as electroless copper plating (the steps so far are called as a full-additive method), and if necessary, subsequent electroplating such as electrolytic copper plating (the steps so far are called as a semi-additive method), thereby forming a printed wiring board. The insulating resin may often contain a silica-based filler, so that the insulating resin can have improved mechanical and electrical characteristics and at the same time the anchor effect in the roughening treatment enhances adhesion between an insulating resin substrate and a plating film. However, there has arisen the problem of a decrease in the adhesion to the plating film as the surface roughness (anchor irregularities) of an insulating resin substrate becomes small with high functionalization and high integration of printed wiring boards.
Under the above circumstances, for example, Japanese Patent Laid-open Publication No. 2010-106337 (hereinafter referred to as Patent Document 1) discloses a conditioner as a pretreatment solution for electroless plating, which is used for treating the surface of a substrate to be used for a printed wiring board and which contains a cationic polymer (or a cationic surfactant), a nonionic surfactant, and ammonium hydrogendifluoride in water. Patent Document 1 above shows, in the section of “Examples”, that when an insulating resin substrate is dipped into a conditioner having the above composition, followed by electroless plating and electrolytic copper plating, peeling strength between an underlying resin and a plating film becomes high to enhance adhesion between the resin substrate and the plating film. The conditioner can also be applied to substrates for printed wiring boards, having fine penetrating holes called “through holes” and fine non-penetrating holes called “blind via holes”, and a photograph is also disclosed, in which the adhesion property of copper plating is satisfactory in the inner portions of through holes.
Japanese Patent Laid-open Publication No. 2009-270174 (hereinafter referred to as Patent Document 2) also discloses an etching treatment solution containing a fluorine compound such as hydrogen fluoride as a pretreatment solution for electroless plating, which is used to produce a printed wiring board from an insulating resin substrate containing a silica-based filler in an insulating resin. As demonstrated in Patent Document 2, the use of a fluorine compound-containing treatment solution as described above makes it possible to achieve high adhesion between a treated substrate and a plating film even for substrates having small surface roughness.